In military tanks the gunner and commander each view the target zone through individual mirrors that are swingably mounted within the hull or turret. The gunner or commander adjusts his mirror by actuating controllers for the voltage supply to a torque motor that is drivingly connected to the mirror pivot shaft. At times the torque motor also receives a voltage signal from a gyroscope that responds to vibrational dislocations of the mirror due to terrain disturbances, principally pitching movements about the transverse axis of the vehicle. At such times the torque motor applies a torque to the mirror to keep it reasonably stable in spite of the terrain disturbances.
Under some conditions the torque motor may be unable to keep pace with the mirror dislocation movements. The mirror therefore jiggles or vibrates in spite of the attempted corrections by the motor. The principal reason for this undesirable condition is motor friction and system inertia that oppose rapid reversal of the motor and associated gearing.
The present invention proposes a second gyroscope responsive to terrain disturbances for generating a second motor control signal. This second signal is passed into a zero crossover detector, which produces a square wave output substantially in phase with the main gyro signal. An algebraic summing amplifier combines the two signals into a useful motor control signal that provides increased motor energizer voltage of opposite polarity when the motor is required to reverse its movement direction. The aim is to minimize deadband effects due to motor friction and system inertia.